Light sources such as light-emitting diodes (LEDs) are an attractive alternative to incandescent and fluorescent light bulbs in illumination devices due to their higher efficiency, smaller form factor, longer lifetime, and enhanced mechanical robustness. Such systems typically have multiple LEDs, and optionally other passive or active components, mounted on a printed circuit or wiring board. The printed circuit board may be fiberglass, such as FR4, or, for cases in which higher heat loads must be managed, a metal core printed circuit board (MCPCB). The cost of these systems must be reduced and the reliability improved in order to drive increased market penetration. In order to reduce cost, some systems have utilized low-cost plastic substrates. Such systems may feature conductive traces formed over the plastic substrate (e.g., a plastic wiring board) interconnecting a large array of packaged or unpackaged LEDs. In some cases the plastic substrate is flexible. Such systems have been described in U.S. patent application Ser. No. 13/171,973, filed on Jun. 29, 2011 (the '973 application), the entire disclosure of which is incorporated herein by reference.
One challenge for systems based on plastic substrates is the reduction of mechanical stress on the components mounted on the circuit board. Mechanical stress may cause the joint between the component and the circuit board to weaken or fail, resulting in reduced performance or, in some cases, partial or complete system failure. Mechanical stress may arise from a number of sources, including but not limited to flexure of the substrate and thermal cycles. Thermally induced mechanical stress may arise from, for example, changes in ambient temperature or device self-heating during operation and/or power cycling. Stress reduction is of particular importance for flexible substrates both in operation and during manufacture, where in some cases roll-to-roll manufacture may be contemplated. Broadly stated, stress may arise during manufacture, shipping, operation and/or one or more other stages of the life of a system.
In view of the foregoing, a need exists for systems and techniques enabling the low-cost design and manufacture of reliable array-based lighting systems capable of supporting a large number of different products and having a cost-effective drive and interconnect system. Such lighting systems should preferably also be uniform, reliable, large-area, and low-cost.